/**
 *
 * @param {Function} fn 这个是回调函数,通过懒加载函数,判定滚动条要到达边界阈值的时候,回调这个函数
 * @param {Number} threshold 滚动条到底部的边界阈值
 */
function lazyLoad(fn, threshold = 100) {
  let flag = true;
  window.onscroll = function () {
    let scrollTop =
      document.documentElement.scrollTop || document.body.scrollTop;
    let clientHeight = document.documentElement.clientHeight;
    let scrollHeight = document.documentElement.scrollHeight;
    let scrollBottom = scrollHeight - (scrollTop + clientHeight);
    if (scrollBottom <= threshold) {
      if (flag) {
        flag = false;
        fn();
      }
    } else {
      flag = true;
    }
  };
}
